1. Field of the Invention
The present invention relates to a conductive paste and a ceramic electronic component.
2. Description of the Related Art
Hitherto, a ceramic electronic component has been composed of, for example, a ceramic element assembly, an internal electrode and a terminal electrode. The ceramic element assembly is produced by, for example, baking a green laminate in which a plurality of green ceramic layers made of a dielectric material are laminated. The internal electrode is provided between ceramic layers in the ceramic element assembly and is formed by printing a conductive paste on a plurality of green ceramic layers and by baking the conductive paste concurrently with the green ceramic layers. The terminal electrode is formed by coating the end face of the ceramic element assembly with the conductive paste and by baking the coating film. In order to improve solder wettability and solder heat resistance in mounting the ceramic electronic component on a circuit substrate, etc., the terminal electrode may be subjected to a plating treatment with Ni, Sn, solder, etc.
The conductive paste for forming the terminal electrode contains a conductive component, a glass frit and an organic vehicle. In recent years, base metals such as Ni and Cu, in addition to noble metals such as Ag, Pd, and Ag/Pd, have been used as the conductive component. As the glass frit, Bxe2x80x94Sixe2x80x94O glass frit may be appropriately used.
When the terminal electrode of the ceramic electronic component is formed using a conductive paste containing a conductive component made of a base metal and the terminal electrode is subjected to the plating treatment, however, the plating solution is likely to penetrate into the terminal electrode since the sintering density is lower than that of the terminal electrode formed using the conductive paste containing the conductive component made of such a noble metal as Ag/Pd, and it is feared that internal flaws are generated in the ceramic element assembly so as to cause an internal defect.
As a method for increasing the sintering density of the terminal electrode containing Cu as a conductive component, which has an especially low sintering density, for example, a method in which a baking temperature is increased can be mentioned. However, since the viscosity of softened glass is further decreased, the glass in the coating film flows into the interface between the ceramic element assembly and the electrode or flows on the surface of the terminal electrode during the baking, so that not only does a so-called xe2x80x9cadhesion defectxe2x80x9d, in which ceramic electronic components adhere to each other with glass therebetween, frequently occur, but also the region in the coating film that the glass previously occupied becomes a cavity so as to cause penetration of the plating solution.
A method in which a glass frit having a further increased softening point is used may be suggested. In this case, however, although a liquid phase sintering due to glass and the resulting aforementioned xe2x80x9cadhesion defectxe2x80x9d is not likely to occur, the penetration of the plating solution still occurs due to decrease in the sintering density.
The present invention was made to solve the aforementioned problems. Accordingly, it is an object of the present invention to provide a conductive paste capable of forming a terminal electrode in which the sintering proceeds while the viscosity of the glass is maintained during the sintering of the conductive component, so that the softened glass is prevented from flowing into the interface between the ceramic element assembly and the terminal electrode or from flowing on the surface of the terminal electrode, and furthermore, a sufficient amount of glass remains in the cavity of the terminal electrode film so that an excellent seal is provided against the penetration of the plating solution, and the xe2x80x9cadhesion defectxe2x80x9d is prevented from occurring. It is another object of the present invention to provide a ceramic electronic component provided with the aforementioned terminal electrode.
In order to achieve the aforementioned objects, a conductive paste according to an aspect of the present invention is composed of a conductive component containing at least one of Cu and Ni, a glass frit and an organic vehicle, in which the glass frit contains at least one kind of crystallizable glass, and the sintering starting temperature of the conductive component is higher than the crystallization starting temperature of the crystallizable glass but lower than the remelting temperature of the crystallizable glass.
The aforementioned crystallizable glass is preferably Bxe2x80x94Sixe2x80x94Xxe2x80x94O glass, where X is at least one alkaline-earth metal.
The aforementioned crystallizable glass is also preferably Bxe2x80x94Sixe2x80x94Xxe2x80x94Yxe2x80x94O glass, where X is at least one alkaline-earth metal and Y is at least one member selected from the group consisting of Al, Cu, Ni, Zn, Mn and alkali metals.
A ceramic component according to another aspect of the present invention is provided with a ceramic element assembly and a terminal electrode formed so as to contact with the ceramic element assembly, in which the terminal electrode is formed using the aforementioned conductive paste according to the present invention.